Tunneling processes in double-barrier GaAs/AlAs diodes with an incorporated AlGaAs pre-barrier were studied under hydrostatic pressure. The electrical characteristics resulting from a pre-barrier on the side of the emitter can be explained at 1 bar, solely by the Γ-profile: increasing pressure shows that the pre-barrier does not reduce the Γ-X tunneling. A pre-barrier on the collector side leads to charge buildup at the X minimum within the AlAs collector barrier.